Hmmm good thread, we've been talking about this at the Zeros shop.
My PP Derbi has the 65 Metra, TjT, stock contra, vm18, currently has a 65 Zen pipe, formally had a Ninja circuit, oh and yellow springs
it starts with a quarter kick, or a slight push, the carb is dialed in perfect
BUT it his a wall, around 45 maybe a bit higher it just flattens out and hangs there, off the line its insane, pulls like a monster, but then it just, well stays at 45ish. We recently tuned a stock PP motor, didnt touch the cylinder, added a 14/12 (15sha is on the way), DOS vario, with the Ninja circuit it did 38-39, we added some clutch springs and a Tomos BK100, it now does 41, but feels exactly the same, just hits a wall.
Now Im thinking this is a just a thing with the PP motor? I have a very similar set up on my PR Derbi, 65 Metra, malossi reeds, TjT, Tomo Estoril, 15 sha, however while the low end is great, its got nothing on my PP, this bike does high 40's touches early 50's with no wind, however im running a Pietcard set up on my PR Derbi, maybe its all in the ignition?